Goals are to study the development and progression of precancerous cytologic and histo-pathologic changes of the anal epithelium among HIV-positive and negative homosexual men, to identify risk factors, perform dose escalation studies of isotretinoin and interferon-alpha, determine efficacy of prevention recurrence by (1)ablation alone, (2) ablation in combination with isotretinoin, and (3) ablation in combination with isotretinoin and interferon-alpha.